1. Field of the Invention
The present invention relates to an ADM (Add Drop Multiplexing) system wherein ADM devices are connected by multistage connections with SONET (Synchronous Optical NETwork), SDH (Synchronous Digital Hierarchy) or Ethernet (registered trademark).
2. Description of the Related Art
Conventional ADM systems implementing SONET/SDH are relayed in multi-stages when hierarching storage stations or providing long-haul trunks. However, management operations are generated for every trunk segment when increasing or reducing path speed. In recent years, with the diffusion of corporate L2 services (service providing layer 2 connection between points) and ADSL, systems which transmit Ethernet (registered trademark) traffic using ADM systems are being constructed. Furthermore, with the future diffusion of FTTH (Fiber to the Home), the reception of Ethernet (registered trademark) traffic to ADM systems is expected to increase-drastically.
ADM systems are generally constructed by implementing SONET or SDH. Although SDH is described in order to simplify explanation, the same also applies to SONET.
Link capacity adjustment scheme (LCAS) function is a function which increases or reduces path speed. ADM systems which increase and reduce the speed of trunk path bands in conjunction with an opposing device using this LCAS function are also disclosed.
FIG. 1 is a diagram explaining the operating conditions of the LCAS function in conventional ADM systems.
In FIG. 1, Pattern 1 shows opposing Ethernet (registered trademark) signals when enclosed within a single segment; Pattern 2 shows a case wherein trunk a connection is made by Ethernet (registered trademark); and Pattern 3 shows a case wherein a trunk connection is made by SDH.
Of these three patterns, LCAS function operation within the ADM system is possible only in Pattern 1. In Pattern 1, the transmission of LCAS control information is performed within the ADM segment by transmitting/receiving control codes within an H4 byte area in the POH (Path Over Head).
In addition, in actual systems, many are constructed such that ADM systems are relayed in multi-stages as in Pattern 2 and Pattern 3 to transmit signals.
Furthermore, technologies which transmit working traffic using working channels and protection channels by the LCAS function if the ring network is normal and circumvents interference generation area in conjunction with the protection function if interference exists are disclosed (for example, refer to Japanese Patent Publication; Japanese Patent Laid-open Publication No. 2002-359627).
However, in the above Pattern 2, because POH is terminated within the ring in the Ethernet (registered trademark) interface which is connected by trunk connection, the H4 byte transmitted and received in the ADM segment cannot be relayed in the Ethernet (registered trademark) trunk connection segment (*1 in FIG. 1), and therefore, the LCAS function cannot be operated end-to-end simultaneously between plural ADM systems.
Furthermore, in Pattern 3, although an H4 byte is relayed in an SDH interface used in trunk connection, the LCAS function cannot be operated end-to-end because there is no system for monitoring and controlling the H4 byte.
The factors which make the LCAS function inoperable in Pattern 2 and Pattern 3 are as follows:
(1) H4 byte transmitted and received in ADM segments cannot be relayed to the trunk connection segments in the trunk-connected Ethernet (registered trademark) interface, and therefore, the LCAS function cannot be operated simultaneously between plural ADM systems.
(2) Although an H4 byte is relayed in an SDH interface, the LCAS function cannot be operated because there is no system for monitoring and controlling the H4 byte.
Therefore, when increasing and reducing the speed of the trunk path bands in Pattern 2 and Pattern 3, the operator must set paths by manual operation for each device and each segment, thereby exacerbating operation efficiency. This was also the cause of increase in operation costs.